whats special about the atrial and ventricular muslce fibers?

they contract longer than skeletal muslce

what are intercalated discs?

connections between heart muscle cells. they have gap junctions

What does the AV bundle do?

transmits conduction from atrium synctium to ventricular. It allows the atria to contract before the ventricles

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Cardiac action potential

~105 millivolts, The intracellular potential rises from -85 to +20 mv during each beat. The membrane remains depolarized for about .2 seconds( plateau)

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Whats the reason for the plateau in action potential?

allows the ventricular contraction to be as much as 15 times longer than skeletal muscle

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what allows the cardiac fibers to have a prolonged AP plateau?

instead of just sodium channels opening they have calcium-sodium channels ( slow calcium channels) The slow channels maintain the depolarization period which causes the plateau

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what else allows the cardiac fibers to have a prolonged AP and plateau?

after the onset of the AP the permeability of cardiac fibers for potassium ions decreases about 5 fold which doesnt happen in skeletal muscle. This decreases the outflux of potassium ions which prevents early return.

.3-.5 seconds. This is slower than nerve fibers and skeletal fibers

whats a problem with Tachycardia in regards to the atria?

P wave

depolarization through the atria and followed by atrial contraction. This causes a slight rise in atrial pressure

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QRS waves-

depolarization of Ventricles and causes the ventricular pressure to begin rising

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T wave-

repolarizing of the Ventricles and ventricular muslce starts to relax

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Atria as primers

~80 % of blood flows directly through ventricles even before contraction. The Atria simply act as primers that increase ventricular pumping effectiveness as much as 20%.

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A wave-

Atrial contraction

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C wave

ventricles begin to contract and blood backflows into atria

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V wave

occurs toward the end of ventricular contraction. This is when blood is slowly filling the atria while the AV valves are closed

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Period of rapid filling of ventricles

blood pushes AV valves open and fills the ventricle during the first 1/3 of diastole. Middle 1/3 of diastole involves blood straight from the veins into the ventricles. Last 1/3 of diastole is when the atria contract accounting for an additional 20% of filling

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isovolumic contraction

period between when the AV valves close and the ventrilces contract and push the semilunar valves open.

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End diastolic volume

normal filling of ventricles. about 110-120 ml

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stroke volume output

when ventricles contract and empty to about 70ml

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end systolic volume

remaining volume in each ventricle after contraction. about 40-50 ml.

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ejection fraction

fraction of end diastolic volume that is ejected from the heart( jusually about 60%)

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in regards to end diastolic and end systolic volume, how can stroke volume increase?

increase end diastolic and decrease end systolic volume

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Semilunar valves functions

Pressure from arteries close them rapidly.

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first heart sound

closure of AV valves. Low pitch and long lasting

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second heart sound

aortic and pulmonary valves closing. High pitch and fast

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stroke work output

amount of energy the heart converts to work during each heartbeat

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minute work output

total energy converted in one minute.

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work output of heart

spends energy on moving blood from low to high pressure. Also spends energy speeding blood to its velocity of ejection through the valves

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the problem with having high systolic pressure

it pushes the actin and myosin filaments far apart and they stop working optimally

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period of filing

volume increases as blood is pumped into ventricle

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period of isovolumic contraction

all valves are closed so volume doesnt change but pressure does increase because the ventricles are contracting

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period of ejection

systolic pressure rises even higher because of ventricular contraction . Volume is decreasing because the aortic valve is now open

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period of isovolumic relaxation

aortic valve closes and ventricles fall back to starting point which is about 50 mmHg

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How the heart gets energy

70-90 % is from metabolizing fatty acids. 10-30% from other nutrients like lactate and glucose

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external work of the heart

oxygen consumption and chemical energy expended during contraction

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potential energy of the heart

additional work that could be accomplished by contraction of the ventricle if the ventricle were completly emptied

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what is the maximum efficency of the normal heart?

20-25 % . heart failure can go as low as 5-10%

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Frank starling mechanism

The greater the heart muscle is stretched during filling, the greater the force of contraction it gives

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sympathetic mechanism on heart

cause the heart to double its output

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parasympathetic mechanism on heart

Vagus nerve, Can stop the heart for a couple seonds. Decrease pumping as much as 30% below normal

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potassium ion effect

excess extracellular ions cause the heart to dilate and become flacid which slows the rate. Also block conduction system through AV node